Unable to change theme to FlowingDark???

Hi everyone,
I want to apply FlowingDark theme to my page but I am unable to do it so.I went in themes and choose FlowingDark theme and saved it but still the theme of my page isn't changing?What could be the problem??I am using this script through softaculous.Please help me!!

Most probably, phpAlbum can

Most probably, phpAlbum can not write the database files. Change all files in your data directory to CHMOD 666, so that apache/php-user can write it.

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